The Moon is getting an airport, and airports run on schedules. A plane taxis, waits its turn, and lands only when a gate opens up.

Spacecraft headed there will soon need that same kind of order, minus the runway, the tower, and anything that ever holds still. Within the next two decades, NASA’s Gateway is expected to become humanity’s first lunar spaceport. Orion crew capsules, landers, cargo ships, and astronauts will pass through it on their way between Earth, the lunar surface, and eventually farther into deep space. No crackling intercom will ever announce a gate change there.

Instead, every vehicle near Gateway will follow an invisible path shaped by the gravitational pull of Earth and the Moon. Someone has to work out who moves where and when. That is the job that a team of engineers from Texas A&M University, NASA’s Johnson Space Center, and Purdue University set out to do. Dr. Diane Davis, an associate professor of space engineering at Texas A&M, led the group that developed the algorithms and operating rules needed to keep multiple spacecraft safely separated around Gateway.

“The future of lunar exploration depends as much on the traffic management as it does on the rocket science,” Davis said. Gateway will not circle the Moon the way a satellite circles Earth. It will travel in a near-rectilinear halo orbit, or NRHO, an elongated path shaped by the combined gravity of Earth and the Moon rather than by the Moon alone.

“The Gateway NRHO is a nearly stable and highly elongated orbit around the moon that provides an uninterrupted line of sight for communications to Earth and requires little propellant to maintain,” Davis said. The orbit swings within 1,000 miles (1,609 kilometers) of the Moon’s north pole before looping nearly 40,000 miles (64,374 kilometers) beyond its south pole. No crewed spacecraft has ever followed a path quite like it.

A lone station can maintain that course with occasional engine burns. Add an arriving Orion capsule, an uncrewed cargo ship, and a lander all trying to dock or park nearby, and keeping every vehicle clear of the others becomes much harder. “Collisions and serious damages could happen,” Davis said. “To ensure crew safety and mission success, effective traffic management in the NRHO is crucial.”

The fix the team built centers on something they call loitering. “Loitering in space means maintaining a spacecraft relative to a specific orbit or trajectory without executing an immediate maneuver,” Davis said. Before docking or leaving, a vehicle may have to wait hours, days, or even weeks for a port to open or another mission to wrap up.